Sensor for measuring hydraulic fluid pressure of a diaphragm compressor

ABSTRACT

A pressure sensor having a housing connected to a compressor head, the housing including a piston movably mounted in a cylinder, the cylinder is fluidly connected to a high-pressure part of a hydraulic system of the compressor, where the piston is adapted to be moved in a first direction away from the compressor head by the pressure of the hydraulic fluid in the high-pressure part, thereby moving a displacement member which is movably attached to the housing by one or more flexible suspensions, and the piston is adapted to be moved in a second direction towards the compressor head by the flexible suspension via the displacement member.

TECHNICAL FIELD

The present disclosure relates to diaphragm compressor having a sensorfor measuring the hydraulic pressure of the diaphragm compressor and amethod of controlling the diaphragm compressor based on said pressuremeasurements.

BACKGROUND

In a diaphragm compressor for pressurizing a fluid the diaphragm isseparating a lower hydraulic fluid chamber and an upper fluid chamber.The hydraulic fluid chamber is part of a hydraulic fluid systemestablishing a pressure in the hydraulic fluid chamber by moving apiston. The pressure makes the diaphragm moving towards the fluidchamber thereby pressurizing the fluid hereof. To ensure fulldisplacement of the diaphragm and to compensate e.g. for leakage at thepiston, hydraulic fluid is injected each cycle. When the diaphragmreaches full displacement and the piston has still not finished itsdischarge stroke, the excess hydraulic fluid in the hydraulic fluidchamber exits the hydraulic fluid chamber and via a passage conducted toa hydraulic fluid reservoir of the hydraulic fluid system.

The known systems have the drawback that the exit of the excesshydraulic fluid leads to loss in efficiency of the compressor.

BRIEF SUMMARY

The present disclosure solves the problem with controlling the maximumhydraulic fluid pressure by a compressor and control hereof according tothe inventive method described below.

The disclosure relates to a pressure sensor comprising a housingconnected to a compressor head, the housing comprising a piston movablymounted in a cylinder, the cylinder is fluidly connected to ahigh-pressure part of a hydraulic system of the compressor, wherein thepiston is adapted to be moved in a first direction away from thecompressor head by the pressure of the hydraulic fluid in thehigh-pressure part, the piston is thereby adapted to move a displacementmember which is movably attached to the housing by one or more flexiblesuspensions, and wherein the piston is adapted to be moved in a seconddirection towards the compressor head by the flexible suspension via thedisplacement member.

The pressure sensor is advantageous in that it functions as anoverpressure protection at the same time as a pressure sensor. This isbecause the flexible suspension is able to at least temporary absorbpressure increase from the high-pressure part of the hydraulic system ofthe compressor.

According to an embodiment of the disclosure, the flexible suspensionsare implemented as an array of bolts and springs. This implementation isadvantageous in that the springs temporary absorbs the pressure from thehydraulic system in one part of the compression cycle and in anotherpart of the compression cycle returns the absorbed pressure to thehydraulic system.

According to an embodiment of the disclosure, the pressure sensorfurther comprise a displacement sensor adapted to detect the distance ofthe movement of the displacement member. The compressor comprises ahydraulic system creating a hydraulic pressure which via the diaphragmis pressurizing the gas. The part of the hydraulic systems creating thehigh-pressure moving the diaphragm is referred to as high-pressure partand is located between the valve and the pressure sensor. In the idealscenario, the peak pressure of the hydraulic fluid is just enough tomove the diaphragm to a position where all of the gas is leaving the gaschamber.

The pressure sensor is adapted to measure the pressure in thehigh-pressure part. This can be done in various ways hence the pressuresensor may at least be adapted to measure a displacement caused by thepressure and/or a flow of excess hydraulic fluid from the high-pressurepart. Accordingly, the feedback signal is either by the pressure sensoror a controller converted to a pressure which is comparable to the peakpressure value.

The housing is preferably connected to the high-pressure part of thehydraulic system of the compressor. It is advantageous in that itsconnection point to the compressor is not limited to a specific locationof the compressor head as long as it is able to fluidly communicate withthe hydraulic fluid of the high-pressure part.

The fluid connection/communication path between the high-pressure partand the cylinder is preferably a straight conduit to ensure straightflow of the hydraulic fluid to be able to obtain the most accuratemeasurement of the pressure.

The displacement member is preferably mounted to the housing by flexiblesuspensions the load of which is equal to or less than the pressure ofthe hydraulic fluid when the piston is just before the so-called topdead center of a pressure curve of a compression cycle. This ensuresdisplacement of the displacement member before the compression reachesits top dead center.

The displacement member is preferably a massive block of a metalsuitable to withstand the pressure from the piston in one direction andfrom the suspensions in the opposite direction. Preferably the housingis made of the same material and of a thickness of the cylinder wallsthat can withstand the pressure from the hydraulic fluid.

By movable mounted should be understood that the piston is “floating” inthe cylinder i.e. it is preferably not fastened in any of its ends. Atthe second end the piston is simply pushing to the displacement memberwith a pressure equal to the pressure by which the hydraulic fluid ispushing to the first end of the piston. The friction between the pistonseal(s) and cylinder walls can be neglected.

According to an embodiment of the disclosure, the displacement memberand the piston is made of aluminum, preferably an aluminum alloy. Thisis advantageous in that weight of the movable piston and displacementmember is low in mass to accommodate high frequency cyclic movement.This is in contrary to more heavy masses which may disturb the dynamicsbetween movement and pressure ending up in a delayed feedback signal.Low weight is preferably less than 350 grams for a displacement memberhaving a diameter of about 10 centimeters.

According to an embodiment of the disclosure, the center part of thedisplacement member which is in physical contact with the head of thepiston is made of steel, preferably a steel alloy. This is advantageousin that at the contact point between the piston and displacement membera material is used which is more resistant to wear than the aluminum.

According to an embodiment of the disclosure, the shape of the head ofthe piston is spherical and wherein the contact point of thedisplacement member to the piston is concave. This is advantageous inthat hereby is obtained an equal pressure to and from the displacementmember on the piston. Hence, it is not a problem if the suspensions arenot completely evenly loaded.

According to an embodiment of the disclosure, the pressure sensor isconnected to the hydraulic fluid distribution plate or the lowercompressor head. This location is advantageous in that here it ispossible to obtain a short and direct fluid path between the hydraulicfluid and the cylinder of the pressure sensor.

Further, this location is advantageous in that the oil distributionplate and the lower compressor head are large rigid parts to which thepressure sensor can be securely mounted or connected e.g. by means of anarray of bolts.

According to an embodiment of the disclosure, the cylinder end towardsthe displacement member is closed only leaving an opening through whichthe piston can obtain mechanical contact with the displacement member.This is advantageous in that then the piston so to speak is closing theconduit in which the hydraulic fluid is able to leave the high-pressurepart and at the same time the pressure of the hydraulic fluid can betransmitted to the displacement member.

According to an embodiment of the disclosure, the array of flexiblesuspensions is fastening the displacement member to the housing so thatmovement of the displacement member requires a hydraulic fluid pressureabove a displacement pressure. The flexibility of the suspensions can beadjusted either by the choice of springs and/or by the torque with whichthey are held in place between the bolt head and the displacementmember. Preferably each of the suspensions (in a preferred embodimentbolts with springs around the threaded part between displacement memberand the bolt head) are all tightened with the same torque ensure equalload of the piston.

The displacement pressure is preferably less than or equal to thepressure of the hydraulic fluid at the top dead center.

According to an embodiment of the disclosure, the displacement sensor isa distance sensor, preferably an optic distance sensor. An opticdistance sensor is advantageous in that it is very fast i.e. itfacilitates performing at least one distance measurement per compressioncycle i.e. up to 7-800 measurements per second. The optic sensor isconnected to the controller and the distance measurement is transmittedto the controller. The distance measurement is referred to as feedbacksignal. The displacement of the displacement member i.e. the measureddistance is directly linked to pressure of hydraulic fluid in thehigh-pressure part.

According to an embodiment of the disclosure, the displacement sensorprovides the displacement measurements to a controller. Preferably thedisplacement sensor is sending or the controller is scanning the outputof the displacement sensor so that the controller is receiving a signalwhich represents a distance moved by the displacement member.

This distance is by knowledge of a known reference distance linked to aknown pressure and thereby it can be converted to a pressure of thehydraulic fluid. If this pressure is below the pressure peak targetvalue, then the controller controls the injection pump and valve toestablish an injection pressure potential allow an amount of hydraulicfluid to enter the high-pressure part. The amount is determined by sizeof gas inlet pressure, established injection pressure potential and timethe gas inlet pressure is lower than the established injection pressurepotential. The latter will according to an embodiment of the disclosurefacilitate opening an output valve allowing flow from the low-pressurepart to the high-pressure part.

According to an embodiment of the disclosure, the compressor isdiaphragm compressor compressing hydrogen gas to a pressure of at least65 Mpa.

Moreover, the disclosure relates to a hydrogen fueling stationcomprising a compressor.

Moreover, the disclosure relates to a method of controlling the peakpressure of the high-pressure part of the hydraulic system of thediaphragm compressor pressurizing a gas, the diaphragm compressorcomprising: an injection assembly forming part of the hydraulic fluidpath between a low-pressure part of the hydraulic system and thehigh-pressure part, the injection assembly comprising: an output valve,a valve and an injection pump establishing a flow of hydraulic fluidfrom the low-pressure part to the high-pressure part when the outputvalve is open, and a pressure sensor establishing a feedback signalrepresenting the pressure in the high-pressure part, wherein theinjection pump establishing a pressure potential of injection ofhydraulic fluid when the valve is closed and when the output valve isclosed, and wherein a controller is controlling the pressure potentialof injection of hydraulic fluid into the high-pressure part, by controlof the injection assembly based on the feedback signal and a hydraulicfluid peak pressure target value of a desired pressure of hydraulicfluid in the high-pressure part.

According to an embodiment of the disclosure, the pressure potential ofinjection of hydraulic fluid is established in the injection assembly.

According to an embodiment of the disclosure, the amount of hydraulicfluid injected into the high-pressure part in a compression cycle isdetermined by the established potential of injection of hydraulic fluid,wherein the potential of injection of hydraulic fluid is controlled bycontrolling the valve based on the pressure difference between thepressure represented by the feedback signal and the peak pressure targetvalue. Alternatively, the injected amount is simply the amount ofhydraulic fluid that can be injected during a period of time where thepressure in the high-pressure part is below the established injectionpressure potential.

In practice this amount is determined by the size of establishedpotential of injection of hydraulic fluid i.e. the pressure establishedin the injection assembly (i.e. between valve, output valve andinjection pump) and the inlet gas pressure determining the lowestpressure in the hydraulic fluid chamber and thereby if and for how longtime (in a compression cycle) the output valve is open.

Hence a control loop exists where injection pressure potential iscontrolled based on injection of hydraulic fluid and the amount ofhydraulic fluid injected is determined based on the difference betweenthe pressure represented by the feedback signal and the peak pressuretarget value.

Preferably the hydraulic fluid is an incompressible fluid or a fluidhaving an as low compressibility as possible. Oil is preferred in thatsealing's of the compressor piston is lubricated by oil leaking from thehigh-pressure part to the reservoir.

Using the feedback signal representing the pressure in the high-pressurepart to control the amount of hydraulic fluid to inject, is advantageousin that the otherwise non-detectable leakage of hydraulic fluid at thepiston is also compensate for.

According to an embodiment of the disclosure, the pressure is increasedduring a plurality of compression cycles following the compression cycleduring which the feedback signal representing the pressure of thehigh-pressure part was below the peak pressure target value This isadvantageous in that adjusting the pressure in just one compressioncycle following the compression cycle in which the feedback signal wasobtained would require a sophisticated injection assembly. However, incase the pressure is adjusted in the subsequent compression cycle, thewear of the compressor would be reduced.

According to an embodiment of the disclosure, the feedback signalrepresenting the pressure in the high-pressure part is measured in eachcompression cycle.

According to an embodiment of the disclosure, the controller iscontrolling the potential of injection of hydraulic fluid so that thepressure in the high-pressure part is always above a reference potentialwhich is equal to or higher than the inlet pressure of the gas. This isadvantageous in that this prevents the diaphragm from getting in contactwith the bottom of the hydraulic fluid chamber and thereby avoidingcavitation.

The control of the lower pressure is preferably made based on areference pressure measurement obtained from a pressure sensor measuringthe pressure of the gas entering the gas chamber and/or the signal fromthe pressure sensor.

According to an embodiment of the disclosure, the feedback signal isestablished by a pressure sensor comprise a housing mounted to thehigh-pressure part in which a cylinder with a piston in fluidlyconnection with the hydraulic fluid of the high-pressure part islocated, a displacement member and a displacement sensor, wherein thepressure of the hydraulic fluid in the high-pressure part is physicallydisplacing a displacement member and wherein the size of thedisplacement is measured by a displacement sensor. This is advantageousin that it has the effect, that the displacement is equal to the excessof hydraulic fluid in the chamber and thereby a measure for the amountof hydraulic fluid which need to be added (if any).

According to an embodiment of the disclosure, the compressor is used forpressurizing hydrogen gas in a high-pressure storage of a hydrogenrefueling station or of a fuel cell vehicle to a pressure above 35 Mpa.This is advantageous in that refueling of a vehicle tank can be madedirectly from the high-pressure storage or directly from the compressor.

Moreover, the disclosure related to a method of controlling theinjection of hydraulic fluid into a high pressure diaphragm compressorcomprising a hydraulic system, the method comprising: measuring arepresentation of pressure in a high-pressure part of the hydraulicsystem of the diaphragm compressor, and maintaining a desired pressurein the high-pressure part of the hydraulic system by adding hydraulicfluid to the high-pressure part of the hydraulic system under thecontrol of a controller on the basis of said measuring of pressure.

The representation of pressure can in an advantageous embodiment of thedisclosure be made based on a measurement of volume of hydraulic fluidin the high-pressure part of the hydraulic system.

High pressure is preferably understood as a pressure above 10 MPa, i.e.a reference to a high pressure compressor (or simply a compressor) inthis document is to a compressor facilitating pressurizing a gaseousfluid to a pressure of 10 MPA or above.

The high-pressure part of the hydraulic system is preferably referred toas the part of the hydraulic system downstream the injection assemblyhereof more specifically downstream the output valve. In the same way,the low-pressure part of the hydraulic system is preferably referred toas the part of the hydraulic system upstream the injection assemblyhereof more specifically upstream the output valve.

According to an embodiment of the disclosure, the amount of the addedhydraulic fluid to the high-pressure part substantially corresponds tothe amount of leaked hydraulic fluid from the high-pressure part to alow-pressure part of the hydraulic system. This is advantageous in thatthen only a very small amount of hydraulic fluid needs to be added. Thisleads to a more efficient compressor in that energy is only used onpressurizing the needed amount of hydraulic fluid to pressurize themedium such as gaseous fluid. This is in contrast to known systems whereenergy is also used on the amount of hydraulic fluid which exits thehydraulic fluid chamber.

Furthermore, it is advantageous in that since the present disclosureonly injects hydraulic fluid corresponding to what is leaked stress(e.g. related to heat and flow of the excess hydraulic fluid) is reducedon compressor components in that no excess hydraulic fluid have toreturn to the low-pressure part.

In a situation with similar properties of the inlet medium (in itsgaseous or liquid state) to be pressurized such as a gaseous fluid andno other losses to maintain a given outlet pressure of the gaseous fluidthe injected amount should be the same as the leaked amount of hydraulicfluid. If outlet pressure should be increased the injected amount shouldbe higher than the leaked amount and in the same way less if thepressure should be reduced.

The amount (volume) injected to increase pressure is small even one or afew drops of hydraulic fluid more than what is leaked is enough toincrease the hydraulic peak pressure. The hydraulic peak pressure ispreferably required to be higher than the pressure of the medium such asa gaseous fluid.

According to an embodiment of the disclosure, the amount of the addedhydraulic fluid to the high-pressure part is added to the high-pressurepart in discontinued periods of time under the control of the controller8 on the basis of said measured pressure. The discontinued periods oftime are determined by the controller based on the measured pressure inthe high-pressure part and knowledge of a desired peak pressure targetvalue. Accordingly, hydraulic fluid is not necessarily injected in eachcompression cycle. Examples of compression cycles in which injectiondoes not happen could be if desired outlet pressure of the pressurizedmedium is reduced, if properties of the inlet medium such as inletpressure change, etc.

It should be mentioned, that the pressure of the hydraulic fluid in thehigh-pressure part is measured continuously. With this said themeasurement may be “0” value at least during some of the compressioncycle. Preferably, towards the peak pressure of a compression cyclemeasurements are made to be able to determine if in the followingcompression cycle injection of hydraulic fluid is necessary or not.

According to an embodiment of the disclosure, the diaphragm compressorcomprising: an injection assembly forming part of a hydraulic fluid pathbetween the low-pressure part of the hydraulic system and thehigh-pressure part, and a pressure sensor establishing a feedback signalrepresenting the pressure in the high-pressure part, wherein thecontroller is controlling the pressure potential of injection ofhydraulic fluid into the high-pressure part, by control of the injectionassembly based on the feedback signal and a hydraulic fluid peakpressure target value of a desired pressure of hydraulic fluid in thehigh-pressure part.

According to an embodiment of the disclosure, the injection assemblycomprising: an output valve, an injection pump establishing a flow ofhydraulic fluid from the low-pressure part to the high-pressure partwhen the output valve is open, and an injection pump establishing apressure potential in the injection assembly when a valve is closed andthe output valve is closed. The injection assembly comprising components(valve, pumps, etc.) facilitating a controlled injection of hydraulicfrom the low-pressure part to the high-pressure part of the hydraulicsystem.

According to an embodiment of the disclosure, the peak pressure of thehigh-pressure part of the hydraulic system of the diaphragm compressorpressurizing a gas, the diaphragm compressor comprising: the injectionassembly forming part of the hydraulic fluid path between thelow-pressure part of the hydraulic system and the high-pressure part,the injection assembly comprising: the output valve, the valve, and theinjection pump establishing a flow of hydraulic fluid from thelow-pressure part to the high-pressure part when the output valve isopen, and a pressure sensor establishing a feedback signal representingthe pressure in the high-pressure part, wherein the injection pumpestablishing a pressure potential of injection of hydraulic fluid in theinjection assembly when the valve is closed and when the output valve isclosed, and wherein a controller is controlling the pressure potentialof injection of hydraulic fluid into the high-pressure part, by controlof the injection assembly based on the feedback signal and a hydraulicfluid peak pressure target value of a desired pressure of hydraulicfluid in the high-pressure part.

The compressor comprises a hydraulic system creating a hydraulicpressure which via the diaphragm is pressurizing the gas. The part ofthe hydraulic systems creating the high-pressure moving the diaphragm isreferred to as high-pressure part and is located between the injectionassembly and the pressure sensor. In the ideal scenario, the peakpressure of the hydraulic fluid is just enough to move the diaphragm toa position where all of the gas is leaving the gas chamber. It should bementioned that the pressure in the high-pressure part is substantiallythe same in all parts hereof i.e. a feedback signal from the pressure inthe hydraulic fluid distribution plate or hydraulic distribution chambershould be understood as a signal representing the pressure in thehigh-pressure part.

The injection assembly is controlling the injection of hydraulic fluid.To reduce requirements to the injection assembly, the hydraulic fluid isinjected when the pressure in the high-pressure part is lowest. Evensmall (measured in milliliter) quantities of injected hydraulic fluidcan make relatively large pressure increase. The controlled amount ofhydraulic fluid is preferably added as one amount for fast pressureadaption or in portions for a less fast pressure adaption.

The pressure sensor is adapted to measure the pressure in thehigh-pressure part. This can be done in various ways hence the pressuresensor may at least be adapted to measure a displacement caused by thepressure and/or a flow of excess hydraulic fluid from the high-pressurepart. Accordingly, the feedback signal is either by the pressure sensoror a controller converted to a pressure which is comparable to the peakpressure value.

The controller may be any suitable data processor but preferably it is astandard industrial computer such as a programmable logic controller.Preferably the controller determines the peak pressure target value anda bottom pressure value by calculation, lookup tables or viacommunication to a data storage where predetermined values may bestored. Preferably, the controller determines the pressure reference(minimum pressure) by sensor input. Based on the pressure represented bythe feedback signal and the peak pressure target value, the controlleris then able to adjust the injection of hydraulic fluid to obtain adesired pressure of the gas. Control of the injection assembly iscontrol of the components hereof which in an embodiment is output valve,valve and injection pump.

The injection is preferably adjusted by creating a potential ofinjection. The potential of injection of hydraulic fluid into thehigh-pressure part is preferably created by running the injection pumpwhich when the valve is closed will create an increase of the potentiallowest pressure in the high-pressure part. When this pressure increasesto above the lowest pressure in the high-pressure part during acompression cycle injection of hydraulic fluid into the high-pressurepart eventually happens. Hence, the pressure created by the pump is nowthe new lowest pressure in the high-pressure part. If the valvecontinues to be closed and the injection pump continues to run, thepressure continues to increase and the lowest pressure in thehigh-pressure part will again in the following compression cycle beincreased to the pressure established by the running pump by the amountof hydraulic fluid injected into the high-pressure part during thecompression cycle.

The amount of hydraulic fluid and thereby the potential injected ofhydraulic fluid into the high-pressure part can be controlled betweenthe capacity of the pump during one compression cycle and nothing bycontrol of the valve between completely closed and completely opened.Hence, the pressure potential is equal to the pressure in thelow-pressure part when the valve is fully opened (injection pump issimply circulating oil) and fully closed where pressure potential iscontinuing to increase until maximum capacity of the injection pump isreached.

Preferably, the injection potential is created between the injectionassembly/injection pump hereof and the output valve located in thehydraulic flow path downstream the injection pump.

The compression cycle refers to one cycle of the piston of the hydraulicsystem i.e. one intake stroke bringing gas into the gas chamber and onedischarge stroke discharging pressurized gas.

Controlling the injection assembly includes controlling the componentshereof which in a preferred embodiment includes controlling theinjection pump located in the hydraulic fluid path and the valve locatedin the return path (the output valve is preferably pressure regulatedsuch as a check valve).

Determining the hydraulic fluid peak pressure target value of a desiredpressure of hydraulic fluid in the high-pressure part may be dynamic orpredetermined. The adaptive or dynamic determination may be made duringoperation by the controller by look-up tables or calculations e.g. basedon measurements of inlet pressure, outlet pressure, pressure ofhydraulic fluid in the high-pressure part, etc. Alternatively, it may bepredetermined i.e. independent from the control of the compressor e.g.by an engineer designing the control of the compressor.

The disclosure is advantageous in that injecting an amount of hydraulicfluid determined by an established potential to increase the pressurejust as much as needed to reach a peak pressure target value reduces theamount of excess hydraulic fluid leaving the hydraulic fluid chamber.Thereby wear of the system is reduce leading to a compressor having lessfailures and needs fewer service visits compared to similarhigh-pressure compressors.

Further, the efficiency of the compressor is increased in that no energyis lost in getting rid of excess hydraulic fluid of the hydraulic fluidchamber due to the non-controlled hydraulic fluid injection used inknown compressor systems.

Further, when the compressor is in normal operation there is no need fora hydraulic fluid return path from the high to the low-pressure parts ofthe compressor in that only the hydraulic fluid needed to establish adesired pressure is in the hydraulic fluid chamber. The return pathhowever is needed for emergency situations where hydraulic fluid forsome reason have to exit the hydraulic fluid chamber.

Further, the injected hydraulic fluid pressure is also sometimesreferred to as injection pressure and by controlling the amount ofhydraulic fluid so that only the required amount is injected leads atleast to the above-mentioned advantages.

According to an embodiment of the disclosure, the hydraulic flow path isseparated in the high-pressure part and the low-pressure part by anoutput valve. Preferably this valve is a check valve and will bereferred to as such. However, other types of valves such as electroniccontrollable valve, pneumatic or hydraulic controllable valve, etc. canbe used.

The output valve is advantageous in that the pressure potential can beestablished between the output valve and the injection pump which isreleased into the high-pressure part when the inlet gas pressure andthereby the pressure of the high-pressure part is below the establishedpotential.

The output valve is furthermore advantageous in that it protects theinjection assembly from the high pressure created by the compressorpiston. In a situation, the compressor piston may establish a pressureof 100 MPa and the injection pump a pressure of 70 MPa. Accordingly,without the protection of the output valve, due to this difference, thepressure potential would, each time the compressor piston establishes apressure above 70 MPa, be equal to the pressure established by thecompressor piston.

In addition, with reference to the above example, the output valve alsoprevents hydraulic fluid from passing back through the injectionassembly.

According to an embodiment of the disclosure, the hydraulic fluid pathbetween the low-pressure part and the high-pressure part in thelow-pressure part includes a forward path and a return path, wherein thevalve is located in the return path for controlling flow of hydraulicfluid from the injection pump to a hydraulic fluid reservoir. Thelocation of the valve in the return path is advantageous in that bycontrol of the valve facilitates control of the increase of potential ofinjection of hydraulic fluid by closing for the flow of hydraulic fluidin the return path.

According to an embodiment of the disclosure, the forward path fluidlyconnects the injection pump to a hydraulic fluid supply station at leastone inner wall positioned between the hydrogen fluid inlet from thehydraulic fluid reservoir and the forward path and wherein a hydraulicfluid storage volume is located beneath the at least one inner wall.Although it is possible within the scope of the disclosure to connectthe injection pump to the hydraulic fluid reservoir (housing the crankshaft) it is advantageous not to do so. This is because of the movementof the crank shaft, the hydraulic fluid is mixed with air in thereservoir. Accordingly, due to the small amounts of hydraulic fluidwhich is injected per compression cycle even minor air bubbles may leadto difficulties in reaching the desired pressure in the high-pressurepart.

According to an embodiment of the disclosure, the hydraulic supplystation is fluidly connected to the hydraulic fluid reservoir. This isadvantageous in that when the level (e.g. measured by a level sensor) ofhydraulic fluid in the hydraulic fluid reservoir is too high a pump ispreferably used to pump hydraulic fluid from the hydraulic fluidreservoir to the hydraulic supply station.

According to an embodiment of the disclosure, the at least one innerwall is a net with holes between 50μ [mu] and 150μ [mu], preferably 100μ[mu].

According to an embodiment of the disclosure, the at least one innerwall is positioned with an angle of inclination relative to a horizontalbottom plane between 1 and 20 degrees preferably between 2 and 10degrees and most preferably between 3 and 5 degrees. This inner wall isadvantageous in that the perforations are so small that they arefunctioning as air filter for the air bubbles of the received hydraulicfluid. Hence, when the received hydraulic fluid fills up the hydraulicsupply station the air bubbles travels up the inclined perforatedwall(s) whereas the hydraulic fluid penetrates the perforated wall(s).Preferably, the hydraulic supply station comprises two or moreperforated inner walls forming a triangle or funnel through which thehydraulic fluid enters on its way from inlet to outlet of the hydraulicsupply station.

The angle of inclination, diameter and density of holes together withthe storage volume is advantageous in that it allows filtered (includingfiltering air bubbles) hydraulic fluid to be collected in the storagevolume over time from where it can be sucked up by the injection pump.

According to an embodiment of the disclosure, the diaphragm is inphysical contact with the inner surface of the gas chamber prior to thepressure of the high-pressure reaches the pressure peak value. This isadvantageous in that then the diaphragm is discharging all of the gas inthe gas chamber in each compression cycle. It should be mentioned thatthe gas chamber may comprise voids from where minor quantities of thegas cannot escape.

The contact between the diaphragm and the inner surface of the gaschamber is preferably at least made between the inlet port and theoutlet port.

According to an embodiment of the disclosure, the peak pressure targetvalue is between 20% and 15%, preferably between 15% and 10%, mostpreferably between 10% and 5% above the desired pressure of the gasleaving the chamber 14.

It is advantageous to control the pressure of the gas leaving the gaschamber by controlling the pressure of the hydraulic fluid in thehigh-pressure part. This is because the pressure of the pressurized gasis less stable compared to the pressure of the hydraulic fluid. Hence toavoid calculations, compensations etc. to obtain a precise and reliablecontrol loop it is preferred to use the pressure of the hydraulic fluidin the high-pressure part as feedback in the control loop. To be able todo so sufficient movement of the displacement member to create aresolution of the measurements which is sufficient to use in the controlrequires a pressure peak target value some percentage above the desiredoutlet gas pressure.

Further, to be sure to obtain a feedback signal, the pressure peaktarget value is higher than the desired pressure of the gas leaving thegas chamber.

According to an embodiment of the disclosure, the controller iscontrolling the injection of hydraulic fluid into the high-pressure partso that injection is possible during the intake stroke of a compressioncycle where the pressure of the hydraulic fluid in the high-pressurepart is being reduced. Injecting hydraulic fluid in the beginning of thecompression cycle following the compression cycle where the feedbacksignal indicated a pressure increase was needed is advantageous in thatthe requirements to the injection pump is reduce. This is because at thebeginning of a compression cycle the pressure in the high-pressure partis low. It should be mentioned that the injection of hydraulic fluidrequires that the output valve opens and which according to anembodiment of the disclosure is the case when the established potentialupstream the output valve is higher that the pressure downstream theoutput valve.

According to an embodiment of the disclosure, the pressure sensorcomprise a housing mounted to the high-pressure part 1 in which acylinder with a piston in fluidly connection with the hydraulic fluid ofthe high-pressure part is located, a displacement member and adisplacement sensor, wherein the pressure of the hydraulic fluid in thehigh-pressure part 1 is physically displacing a displacement member andwherein the size of the displacement is measured by a displacementsensor.

The displacement based pressure sensor is advantageous when used on acompressor controlled according to the present disclosure. This isbecause the inventive control only injects a very small amount ofhydraulic fluid leading to only a very small amount of excess hydraulicfluid. Hence because the amount is so small, a flow is difficult tomeasure. Instead since the excess amount is so small it is possible toguide it to a cylinder of the pressure sensor where it activates apiston, where it again activates the displacement member according tothe pressure of the hydraulic fluid.

According to an embodiment of the disclosure, the displacement member ismovably mounted to the housing by means of an arrangement of springs andbolts. The electromagnetic force is advantageous in that this enableselectrically adjustable of the force (and thereby hydraulic fluidpressure) which is needed to displace the displacement member.

The mechanical arrangement with bolts holding springs between the bolthead and the displacement member is advantageous in that it does notrequire any control i.e. the force needed from the hydraulic fluidpressure to displace the displacement member is constant. Accordingly,the processing of the size of the displacement is less complicated.

According to an embodiment of the disclosure, the pressure sensor is apressure control valve connected to the high-pressure part comprising aflow sensor for measuring an amount of hydraulic fluid leaving thehigh-pressure part. The pressure control valve could be a spring-loadedvalve opening for flow of hydraulic fluid at a pressure determined bysafety margins of the compressor design.

Even though this is possible Feedback may also come from measurement ofpressure of the gas, however it is preferred to obtain feedback from theexpansion chamber in that this is more precise to the amount of excesshydraulic fluid and thereby the control of the amount of injectedhydraulic fluid can be controlled more precisely.

According to an embodiment of the disclosure, the pressure sensor isconnected to the hydraulic fluid distribution plate or to the hydraulicfluid chamber. Due to the high working pressure of the compressor thepressure sensor needs to be securely connected to the compressor. Theeasiest way of doing so is by means of bolts to either the hydraulicfluid chamber or the hydraulic fluid distribution.

According to an embodiment of the disclosure, the displacement sensor isa distance sensor, preferably an optic distance sensor. An opticdistance sensor is advantageous in that it is very fast i.e. itfacilitates performing at least one distance measurement per compressioncycle i.e. up to 7-800 measurements per second. Furthermore, an opticsensor is accurate in its measurements.

The optic sensor is connected to the controller and the distancemeasurement is transmitted to the controller. The distance measurementis referred to as feedback signal. The displacement of the displacementmember i.e. the measured distance is directly linked to pressure ofhydraulic fluid in the high-pressure part.

Alternative sensor types which may be used includes inductive andultrasonic sensors.

According to an embodiment of the disclosure, the displacement sensorcertified to be located in an explosive atmosphere. Since the preferredgas to compress is hydrogen, the atmosphere in which the compressor islocated is explosive. Accordingly, the displacement sensor should besafe to use in such area. This can be obtained by sealing the sensorhousing, using low power measurement module and communication module,etc.

According to an embodiment of the disclosure, the feedback signal is atleast received when the diaphragm is in the upper half of its movementtowards the inner surface of the gas chamber. Preferably there is nofeedback signal from the pressure sensor when the pressure of thehigh-pressure part is a certain level below the peak pressure targetvalue. Preferably, only when the diaphragm is on the last part of itsway to the top position (referred to as top dead center) and cannotincrease the pressure of the gas in the gas chamber anymore, thepressure increase in the high-pressure part is measured by the pressuresensor.

Together with the controlled injection of hydraulic fluid, according toan embodiment of the disclosure this is advantageous in that then noreturn path for the hydraulic fluid to the low-pressure part of thehydraulic system is needed during normal operation.

According to an embodiment of the disclosure, the gas is hydrogen.

According to an embodiment of the disclosure, the hydraulic fluid is ahydraulic oil.

Moreover, the disclosure relates to a diaphragm compressor forpressurizing a gas to a pressure above 10 MPa, the diaphragm compressorcomprising: an injection assembly forming part of a hydraulic fluid pathbetween the low-pressure part of the hydraulic system and thehigh-pressure part, a pressure sensor adapted to establish a feedbacksignal representing the pressure in the high-pressure part, and acontroller adapted to control the injection assembly so as to establisha pressure potential of injection of hydraulic fluid based on thefeedback signal and a hydraulic fluid peak pressure target value of adesired pressure of hydraulic fluid in the high-pressure part.

According to an embodiment of the disclosure, the injection assemblycomprising:

-   -   an output valve, a valve, and an injection pump adapted to        establish a flow of hydraulic fluid from the low-pressure part        to the high-pressure part when the output valve is open, wherein        the injection pump is furthermore adapted to establish a        pressure potential in the injection assembly when the valve is        closed and the output valve is closed.

According to an embodiment of the disclosure, the pressure potential ofinjection of hydraulic fluid is established in the injection assembly.

Moreover, the disclosure relates to a hydrogen fueling stationcomprising a first hydrogen storage and a second hydrogen storage and acompressor having an oblong shaped chamber moving hydrogen in a firstpressure of the first hydrogen storage to a second pressure in thesecond hydrogen storage, wherein the compressor is controlled.

Moreover, the disclosure relates to a compressor comprising a pressuresensor.

BRIEF DESCRIPTION OF THE FIGURES

In the following, a few exemplary embodiments of the disclosure aredescribed with reference to the figures, of which

FIG. 1 illustrates an example of a prior art compressor

FIG. 2 illustrates an example of a compressor according to an embodimentof the present disclosure

FIG. 3 illustrates a pressure sensor according to an embodiment of thepresent disclosure, and

FIG. 4 illustrates a pressure curve of a compression cycle according toan embodiment of the present disclosure.

DETAILED DESCRIPTION

FIG. 1 illustrates an example of a prior art type of control of thehydraulic pressure in a diaphragm compressor. A pump is simply pumpingoil from the hydraulic fluid reservoir into the oil chamber and asexplained, when the diaphragm reaches its maximum, the excess oil exitsthe oil chamber via a return path to the reservoir. The amount of oilpumped into the oil chamber is the same for each compression cycle and“enough” to ensure that some quantity exist the oil chamber and therebymaximum pressure have been reached.

FIG. 2 (and the other figures) illustrates a preferred embodiment of thepresent disclosure, hence the description in relation to the figuresshould only be understood as such leaving room for changes to thedescription still being within the scope of the disclosure.

A compressor 2 having an upper compressor head 24 in which a gas chamber14 is present and a lower compressor head 25 in which a hydraulic fluidchamber 26 is present.

The upper compressor head 24 has a gas inlet port 27 and a gas outletport 28. The pressure of the gas inlet may be measured by a pressuresensor 29.

The lower compressor head 25 is part of a high-pressure part 1illustrated above the dot/dash line. Hence, the high-pressure part 1 isfound downstream the injection assembly 3 including part of a hydraulicfluid flow path, hydraulic distribution plate 22, hydraulic chamber 26and part of the compressor cylinder 31 above the compressor piston 32and a pressure sensor 7.

Illustrated is also an emergency vent line 33 from the high-pressurepart 1 to the hydraulic fluid reservoir 11 (referred to as reservoir).Flow in the emergency vent line 33 is controlled by an emergency valve34. The emergency valve 34 is preferably controlled mechanically so thatif the pressure of the exceeds a predetermined value the emergency valve34 opens and pressure is reduced in the high-pressure part 1 a hydraulicfluid exits to the reservoir 11. Accordingly, this emergency vent lineis not part of control of the hydraulic pressure in the high-pressurepart 1 but is only used in case of emergency as a so-called second stageoverprotection.

Below the dot/dash line dividing the hydraulic system at the outputvalve 38 and compressor piston 32 is the low-pressure part 4. Hence thelow-pressure part 4 is found upstream the injection assembly 3 includingpart of a flow path, reservoir 11, hydraulic fluid supply station 12(referred to as supply station) and connection hereto illustrated by apump 35. The pump 35 facilitates pumping hydraulic fluid from thereservoir 11 to the supply station 12. In addition, the connection maycomprise not illustrated filters or venting components.

It should be mentioned, that the pressure in the part of the hydraulicflow path downstream the injection assembly 3 is normally higher thatthe pressure of the part upstream the injection assembly 3. Normally,the pressure in the injection assembly 3 (between the injection pump 5,valve 6 and output valve 38) is close the to the gas inlet pressure sothat an increased pressure (pressure potential) above this pressure canbe established fast.

The output valve 38 is preferably a check valve or another kind ofmechanically controlled pressure valve but could also be an electricallycontrolled valve.

The pump 35 is controlled by a level sensor 36. When the level ofhydraulic fluid in the reservoir 11 is above a predefined level, thehydraulic fluid is pumped to the supply station 12. As illustrated, thesupply station 12 comprise diagonal like walls 37 through which thehydraulic fluid has to travel. Therefore, the walls 37 are perforated ordesigned as a net having meshes between 50μ [mu] and 150μ [mu],preferably 100μ [mu]. The walls 37 may be implemented as forming abasket in which the hydraulic fluid from the reservoir 11 enters mixedwith air and when leaving the basket through the walls 37 ending in areservoir without the air. Due to this small size of the holes andsurface tension air bubbles mixed into the hydraulic fluid is filteredaway traveling towards to the top of the supply station 12 leaving airfree hydraulic fluid to be ready to be sucked up into the forward path 9by the injection pump 5.

As illustrated the injection assembly 3 is located in the flow pathbetween the high and low-pressure parts 1, 4. Besides the injection pump5, the injection assembly 3 comprise a valve 6 which is preferablylocated in the return path 10 and the output valve located in the flowpath to the high-pressure part 1.

Preferably, the injection pump is continuously pumping hydraulic fluidfrom the supply station 12 to compensate for leakages at the compressorpiston 32. In addition, the continuous pumping is used to create aninjection pressure potential which is at a level controlled by how muchof the hydraulic fluid is allowed to circulate back to the reservoir 11.

It should be mentioned, that the forward path 9 could also simply beconnecting the reservoir 11 and the injection pump 5. However, due tothe movement of the compressor piston 32 the hydraulic fluid in thereservoir 11 is mixed with air which is then sucked up into theinjection pump 5 and further into the high-pressure part 1. Air is notdesired in the high-pressure part in that it air is compressible i.e.opposite of desired property of the hydraulic fluid hence with air inthe hydraulic fluid the compressed less effective as without.Accordingly, to avoid this the supply station 12 is developed to filterair.

It should be mentioned that the valve 6 could also be located downstreamthe injection pump 5, however this location is not preferred in that itwill lead to less flexibility in control of the injection pump andpressure potential. One reason for this is that the pump then needs tobe stopped when a given pressure potential is reached in order not toexceed it.

A controller 8 is controlling the operation of the compressor. Thecontroller 8 is communicating at least with the injection assembly andthe pressure sensor 7. The same or other controllers may facilitatecontrol of the pump 35, operation of the piston 32, control of the gasin/outlet and other not illustrated elements in relation to operation ofthe controller.

The hydraulic fluid is preferably an incompressible oil which whenleaking around the piston sealing is used for lubrication hereof. Anyfluid having limited compression properties which at the same time mayfacilitate lubrication may in principle be used as hydraulic fluid.

The pressure sensor 7 is on FIG. 2 illustrated as attached to the lowercompressor head 25 including the hydraulic distribution plate 22 andhydraulic fluid chamber 23. In relation to location of the pressuresensor 7 it should be mentioned that it in principle can be locatedanywhere in the high-pressure part 1. Only real limiting factor for itslocation is that it should be able to be firmly attached to comply withthe pressures created by the compressor which may be up to and above 100MPa. This makes the lower compressor head 25 the obvious choice.

At FIG. 2 the hydraulic fluid distribution 22 plate has a fluid pathfluidly connecting it to the pressure sensor 7. As mentioned a similarfluid path could connect the pressure sensor 7 to the hydraulic fluidchamber 23 or the hydraulic fluid flow path from the injection assembly3 to the lower compressor head 25.

FIG. 3 illustrates the pressure sensor 7 according to an embodiment ofthe disclosure. As mentioned, it is not important to which part of thehigh-pressure part 1 of the compressor 2 the pressure sensor 7 isattached.

At FIG. 3 the housing 15 of the pressure sensor 7 is illustrated asattached to the lower compressor head 25 by means of bolts 21.Preferably the lower compressor head 25 comprise a threated part and thehousing 15 comprise not illustrated ducts through which bolts 21 canreach the threated part and thereby fastening the housing 15 to thecompressor 2. Other ways of fastening depending on where the housing isconnected to the high-pressure part 1 could also be used.

At the opposite end of the housing 15 a displacement member 18 ismovably attached to the housing 15 by means of flexible suspensions suchas an array of bolt 21/spring 20 arrangements. The torque with which thebolts 21 is tightened and the tension of the springs 20 are determiningfor the movement of the displacement member 18 at a giver pressure.Hence, by adjusting this the movement can be adjusted.

The pressure sensor 7 comprise a cylinder 16 in which a piston 17 ismovable. In one direction, away from the compressor 2 the movement isdetermined by the pressure of the hydraulic fluid and in a seconddirection, towards the compressor 2 the movement is determined by thedisplacement member 18.

At FIG. 3, the piston has moved the displacement member 18 away from thecompressor 2 accordingly, the pressure in the high-pressure part 1 hasreached or is close to its maximum pressure.

Attached to or in relation to the pressure sensor 7 is illustrated adisplacement sensor 19 the purpose of which is to measure the length orsize of the movement of the displacement member 18 caused by the piston17. The displacement sensor 19 is communicating with the controller 8hence a control loop is established where the control of the injectionassembly 3 is made based on feedback from the pressure sensor 7.

Typically, the displacement member 18 is moved less than 1 millimeter.The adjustment of the size of the movement is aligned with a givenpressure during a test phase. Prior to the test phase, an estimate ofthe needed load (spring load, in the embodiment where springs are usedas flexible suspensions) is calculated based on expected pressure of thehydraulic fluid and area of the cylinder 16. Then the springs 20 areadjusted to counter act this load which is also referred to asdisplacement pressure. Accordingly, the pressure acting on the piston 17from the hydraulic fluid have to be higher than the displacementpressure to move the displace member 18.

During the test phase the displacement pressure is fine-tuned e.g. bymechanically adjusting the displacement pressure until a desireddisplacement is found at a desired pressure. The desired pressure isreferred to as pressure peak target value whereas the actual measuredpressure is referred to as pressure peak value. One non-limiting exampleis that at a pressure peak value of 100 MPa, the size of thedisplacement is adjusted to be 0.05 mm [millimeter].

The relation between the size of the measured displacement and thepressure in the high-pressure part 1 is according to a non-limitingembodiment as follows. The springs 20 holding the displacement member 18is fixed so that at a pressure of e.g.

100 MPa the displacement member is moving e.g. 0.05 mm. Accordingly, ifonly 50 MPa is needed the measured displacement should only be 0.025 mm.Therefore, no establishing of injection potential of hydraulic fluidabove inlet pressure is initiated if a displacement of more than 0.025mm is measured.

The pressure drops in the high-pressure part 1 due to leakage at thecompressor piston 32 hence when the measured displacement as consequencehereof drops below 0.025 mm e.g. to 0.020 mm the valve 6 is closedfacilitating establishing potential of injection of hydraulic fluid intothe high-pressure part 1.

The establishing of the potential of injection is simply made by closingthe valve 6 during one or more preferably successive compression cycles.During a compression cycle where the inlet gas pressure is lower thanwhatever pressure established upstream the output valve 38 this willlead to an injection of hydraulic fluid in the high-pressure part. Theinjection happens due to pressure equalization between the part of thehydraulic flow path in which the potential is established (i.e. the partfrom the injection pump 5/(preferably completely closed) valve 6) to theoutput valve 38. This will in the following compression cycle lead to anincrease in the pressure in the hydraulic pressure chamber and therebyto an increased displacement of the displacement member 18 (at least ifthe injected amount is higher than what is leaking via the compressorpiston 32). Hence when the measured displacement again is 0.025 mm orabove the establishing of pressure potential is stopped again by openingthe valve 6.

The injection pressure potential is in the ideal scenario established asfollows. The gas inlet pressure measured by sensor 29 is used asreference pressure (also referred to as reference 0) for the pressurepotential. Accordingly, an injection pressure potential is increased byclosing valve 6 thereby allowing the injection pump 5 to increase thepressure between valve 6, output valve 38 and injection pump 5. Thepressure here continues to increase until it is above the referencepressure which will open output valve 38 allowing an injection ofhydraulic fluid into the high-pressure part 1. Even the smallamount/volume of hydraulic fluid that can be injected in a compressioncycle is enough to increase the peak pressure value in the followingcompression cycle.

If not injection pressure potential is desired the valve 6 is kept openthereby the injection pump 5 only pumps hydraulic fluid from the supplystation 12 to the reservoir 11 without establishing an injectionpressure potential.

Accordingly, in the ideal scenario, the valve 6 is controlling thepressure between valve 6, output valve 38 and injection pump 5 to bejust above or just below the reference pressure.

The simplest way of implementing flexible suspension is the illustratedbolt/spring arrangement. Alternative to the arrangement of bolts 21, onethreaded rod can be used about which the displacement member 18 can beturned thereby moving towards or away from the housing 15 changing thetension on the springs 20. Yet another alternative is to use anelectromagnetic controllable displacement member 18 using theelectricity to control tension from the displacement member 18 on thesprings 20. In the two alternatives one spring may be used at the centerof the displacement member 18.

It should be mentioned that it may be possible to implement anelectronic controllable gearing facilitating an adjustment of the springload of the flexible suspension.

In addition to establishing a feedback signal representing the pressurein the hydraulic fluid chamber 23, the pressure sensor 7 furthermore hasa function of overpressure protection. This is because when thediaphragm 13 is in its top position and pressure is still increasinge.g. due to compressor piston 32 has not reached its top position, thenthis additional volume of hydraulic fluid is pushed into the pressuresensor 7. Here this volume is pushing the piston 17 which again ispushing the displacement member 18 and thereby expanding/increasing thevolume in the cylinder 16. By this additional volume, the pressuresensor 7 is able to absorb the additional volume of hydraulic fluid(pressure is absorbed) and a first state overpressure protection isprovided.

The principle of this first stage overpressure protection is the same asthe principle leading to establishing the feedback signal representingthe pressure in the hydraulic fluid chamber 23 during normal operationof the compressor. Hence, during an abnormal operation of the compressorthe displacement of the displacement member 18 is still measured andprovided to the controller, but now the displacement represents apressure which is above normal operation pressure.

As mentioned, in addition to the first stage overpressure protection asecond stage overpressure protection is also included in the compressordesign. The first stage overpressure protection is limited to absorb afixed amount of hydraulic fluid/pressure which is sufficient to protectthe compressor during normal operation. The fixed amount is equal to apressure which the flexible suspension can absorb.

However, in the unlikely event of failure of the compressor control orpart, the second state overpressure protection (emergency line 33 andvalve 34) is used to relief pressure from the hydraulic fluid chamber 32by leading the hydraulic fluid to the reservoir 11.

FIG. 4 illustrates the principles of a compression cycle according to anembodiment of the disclosure. One compression cycle exists between T1and T6 including one movement up and down of the diaphragm 13. Themovement of the compressor piston 32 is illustrated as the dotted line.

Between T1 and T3 the diaphragm 13 is moving up towards the gas chamber14 thereby pressurizing the gas therein. From T2 the pressure is keptconstant by opening the gas outlet 28 thereby discharging the nowpressurized gas.

At T3, the gas chamber 14 is empty (at least close to, there might besome gas left in the gas chamber in small voids e.g. in relation theinlet port, etc.) and the pressure continues to increase until thecompressor piston 32 is in its top position at T4. As illustrated, thecompressor piston 32 moves up from T1 to T4.

In an embodiment, the pressure sensor 7 comprises a displacement member18 which is moving according to the initial load adjustment of theflexible suspension holding it. In an embodiment, the displacementmember 18 is starting to move at a pressure of e.g. 35 MPa and as thepressure increases towards a pressure peak value of e.g. 80 MPa the sizeof the displacement of the displacement member 18 increases with thepressure increase.

The pressure increase and the displacement of the displacement member isnot necessarily linear in that. In the situation of non-linearity, thecalculations of pressure of a given displacement is more complex than inthe situation of linearity. In practice this may result in thefollowing, if an outlet pressure of the gaseous fluid of 100 MPa isdesired, the pressure peak target value may be 110 MPa to ensuremeasurable displacement of the movement of the displacement member 18.If the desired outlet pressure instead is 50 MPa, the pressure peaktarget value may be 70 MPa.

At T3 where there is no more gas in the gas chamber 14, the pressureincreases again which is measurable as a displacement of thedisplacement member 18.

Typically, the load adjustment of the flexible suspension first enablesmeasurement of displacement of the displacement member 18 when thepressure in the high-pressure part 1 is more than 50% of the peakpressure target value. At FIG. 4, an example of a desired interval ofpressure measured by the pressure sensor 7 is illustrated.

At T4 (referred to as top dead center of the piston 32), the pressurestarts to decrease in that the piston 32 starts to move towards thehydraulic fluid chamber 23. The remaining gas in the gas chamber 14expands, gas is introduced into the gas chamber 14 via the gas inlet 27until the compression cycle ends at T6 to start over again as describedfrom T1.

As described, the disclosure is advantageous in that it is able toreduce the top dead center pressure and thereby the load and therebyincrease the efficiency of the compressor in that no excess hydraulicfluid has to exit the hydraulic distribution plate 22/hydraulic fluidchamber 23. This is obtained by using the feedback from the pressuresensor 7 in the control of the pressure potential established by theinjection assembly 3.

The pressure in the high-pressure part 1 is extremely difficult topredict in that it depends on the how much hydraulic fluid is leakingvia the compressor piston 32 and the inlet pressure of the gas enteringthe gas chamber 14, properties with the gas, etc.

Therefore, the peak pressure target value is chosen to be above thedesired pressure of the pressurized gas leaving the outlet port 28. Thepeak pressure target value should be high enough to facilitate movementof the displacement member 18, but still not higher than the hydraulicfluid causing the extra pressure from T3 to T4 can be absorbed by theflexible suspensions. Preferably the peak pressure target value istherefore about 10% higher than the desired pressure of the pressurizedgas leaving the outlet port 28. The percentage is of course determinedby the dimensions of the pressure sensor 7, cylinder 16 and flexiblesuspensions. An example of difference between outlet pressure of gaseousfluid and pressure peak target value is illustrated on FIG. 3.

The solution invented to balance the load/efficiency optimization andstill be sure to establish the peak pressure is to control the injectionassembly 3 based on feedback from the pressure sensor 7. One example forillustration of the control will now be described.

As mentioned, the minimum pressure in the high-pressure part 1 iscontrolled so that it is equal to or just above the inlet pressure ofthe gas entering the gas chamber 14. The gas inlet pressure ispreferably measure by the pressure sensor 29 and communicated to andused by the controller 8 to establish a pressure reference based onwhich the injection assembly 3 controls the injection pressurepotential. This is to avoid the gas pressure moving the diaphragmtowards the bottom of the hydraulic fluid chamber.

It should be mentioned that if for some reason there is too muchhydraulic fluid in the hydraulic chamber (and thereby too high gasoutlet pressure), then to facilitate a pressure decrease (reduce volumeof hydraulic fluid in hydraulic chamber), the valve 6 is controlled(opened) so that the pressure established by the injection pump 5 isjust below the reference pressure. Thereby no injection pressurepotential is established and thereby no hydraulic fluid is injected intothe high-pressure part 1. The pressure in the high-pressure part willthen drop by the leakage at the piston 32.

Just as long as the pressure established by/in the injection assembly 3is below the reference pressure no hydraulic fluid is injected into thehigh-pressure part 1. How much below doesn't matter.

In an example the gas inlet pressure is 20 MPa and used as pressurereference (0 reference) for the injection potential controlled via theinjection assembly 3. Hence a first purpose of the injection assembly 3is ensuring that the diaphragm do not contact the bottom of thehydraulic fluid chamber 23.

The pressure reference of 20 MPa is in the controller 8 linked to a sizeof displacement of the displacement member 18 which in this examplecould be 1/100 of a millimeter. Accordingly, if the size of displacementmeasured by the pressure sensor 7 at T1/T6 is less than 1/100 of amillimeter the controller 8 via the injection assembly 3 increases thepotential of injection of hydraulic fluid.

A second purpose of the injection assembly 3 is the inject hydraulicfluid in the high-pressure part 1 to increase/control the pressure peakvalue.

The maximum pressure in the high-pressure part 1 is controlled as closeas possible to peak at a peak pressure target value. The peak pressuretarget value is determined to be e.g. 5%45% higher than the pressure ofthe gas leaving the gas chamber. The pressure in the high-pressure part1 is controlled as follows.

The injection pump 5 is preferably running continuously in eachcompression cycle to compensate for the leaking hydraulic fluid at thecompressor piston 32 and for changes in the gas inlet pressure or outletpressure. The amount of hydraulic fluid needed is however as mentionedvery difficult to predict. The present disclosure suggests to usemovement of the displacement member 18 to solve this problem.

Hence, as an example if a displacement of 0.1 mm is measured at apressure of 100 MPa, then a measurement of 0.05 mm represents a pressureof 50 MPa, etc. If the pressure peak target value is determined to be 50MPa and a measurement of less than 0.05 mm is measured, then theinjection assembly 3 is controlled to increase the injection pressurepotential.

Accordingly, during the part of the compression cycle where the outputvalve 38 is closed and the valve 6 is controlled (preferably closed orat least partly closed) to reduce the amount of hydraulic fluid which ispossible to flow through the return path 10. Thereby, an injectionpressure potential is established in the hydraulic flow path between thevalve 6, injection pump 5 and output valve 38 (i.e. in the injectionassembly 3). In this part of the hydraulic flow path, a pressure higherthan the inlet pressure is then established which eventually will openthe output valve 38 and via pressure equalization hydraulic fluid willbe injected to the high-pressure part 1. The volume of the amount ofinjected hydraulic fluid will then increase the pressure peak value, ifnot enough to displace the displacement member at least 0.05 mm thevalve 6 is kept closed for one more cycle and so on until themeasurement of 0.05 mm representing a pressure of 50 Mpa has beenmeasured.

As understood the inventive control is dynamic and is preferablyadjusting the amount of hydraulic fluid in each compression cycle tooptimize the peak pressure in the high-pressure part of the hydraulicsystem of the diaphragm compressor.

In the same way if e.g. gas inlet pressure decreases, to ensure thediaphragm continues to allow as much gas in the gas chamber as desired,the injection assembly 3 may be controlled to reduce pressure/amount ofhydraulic fluid in the high-pressure part 1 by opening (or at leastpartly opening) the valve 6.

Preferably, the piston 17 and displacement member 18 are two independentcomponents, however with this said it should be mentioned, that they maybe made from one piece of material.

As is now clear from the above description that the peak pressure valueof the hydraulic fluid is measured by displacement of the displacementmember 18 of a pressure sensor 7. In relation to a desired peak pressuretarget value, if the peak pressure value is insufficient, this ismeasured by an insufficient displacement of the displacement member 18and the injection potential is increased i.e. the injection pressureestablished by the injection assembly 3 is increased. In the same way inrelation to the desired peak pressure target value, if peak pressurevalue is too high, this is measured by an excessive displacement of thedisplacement member 18 and the injection potential is reduced i.e. theinjection pressure established by the injection assembly 3 is reduced.

As understood from the above description, the disclosure enables acontrol of the peak pressure in the hydraulic system by only adding asmall amount of hydraulic fluid to the hydraulic system more specific tothe high-pressure part 1 hereof. As mentioned in the ideal high-pressurecompressor 2 only leakage between low and high-pressure part 1, 4 is viathe compressor piston 32. Accordingly, the amount (also referred to asvolume) of leaked hydraulic fluid is very small hence to maintainbalance between desired pressure and leaked hydraulic fluid only anequal amount of hydraulic fluid requires to be added. If on the otherhand the pressure needs to be increased, only a small amount (measuredin milliliters or drops) more than the leaked amount needs to be added.

The pressure sensor 7 preferably does not measure pressure of thehydraulic fluid directly but instead measures volume of the hydraulicfluid. Since the hydraulic fluid is incompressible when exposed to apressure, the volume stays the same. This leads to displacement of thedisplacement member 18 of the pressure sensor 7 since it is in fluidlycommunication with the high-pressure part 1. During test andcalibration, a given displacement is linked to a given pressure and inthis way by observing the displacement the pressure of the hydraulicfluid is established.

A further advantage of the present disclosure is that because the amountof injected hydraulic fluid is controlled, it is possible to determinethe amount of hydraulic fluid leaking via the compressor piston 32. Thisinformation may be used to determine state of health of at least thepiston and piston seals. When the injected amount of hydraulic fluid(compensated for change in inlet/output pressure) is monitored overtime, at least a tendency of increase injection of maintain a giverpressure can be established. Such increase may indicate that the sealsmaybe are damaged or defect. The latte may be observed if the tendencyof the amount of hydraulic fluid injected starts to increase with asteeper slope.

The above described method of controlling the peak pressure of thehydraulic fluid enables a wider range of operation speeds compared toknow injection systems for compressor.

1. A pressure sensor comprising a housing connected to a compressorhead, the housing comprising a piston movably mounted in a cylinder, thecylinder is fluidly connected to a high-pressure part of a hydraulicsystem of the compressor, wherein the piston is adapted to be moved in afirst direction away from the compressor head by the pressure of thehydraulic fluid in the high-pressure part, the piston is thereby adaptedto move a displacement member which is movably attached to the housingby one or more flexible suspensions, and wherein the piston is adaptedto be moved in a second direction towards the compressor head by theflexible suspension via the displacement member.
 2. A pressure sensoraccording to claim 1, wherein the flexible suspensions are implementedas an array of bolts and springs.
 3. A pressure sensor according toclaim 1, wherein the pressure sensor further comprise a displacementsensor adapted to detect the distance of the movement of thedisplacement member.
 4. A pressure sensor according to claim 1, whereinthe displacement member and the piston is made of aluminium.
 5. Apressure sensor according to claim 1, wherein the center part of thedisplacement member which is in physical contact with the head of thepiston is made of steel.
 6. A pressure sensor according to claim 1,wherein the shape of the head of the piston is spherical and wherein thecontact point of the displacement member to the piston is concave.
 7. Apressure sensor according to claim 1, wherein the pressure sensor isconnected to the hydraulic fluid distribution plate or the lowercompressor head.
 8. A pressure sensor according to claim 1, wherein thecylinder end towards the displacement member is closed only leaving anopening through which the piston can obtain mechanical contact with thedisplacement member.
 9. A pressure sensor according to claim 1, whereinthe array of flexible suspensions is fastening the displacement memberto the housing so that movement of the displacement member requires ahydraulic fluid pressure above a displacement pressure.
 10. A pressuresensor according to claim 1, wherein the displacement sensor is adistance sensor.
 11. A pressure sensor according to claim 1, wherein thecompressor is a diaphragm compressor compressing hydrogen gas to apressure of at least 65 Mpa.
 12. A hydrogen fueling station comprising afirst hydrogen storage and a second hydrogen storage and a compressorhaving an oblong shaped chamber moving hydrogen in a first pressure ofthe first hydrogen storage to a second pressure in the second hydrogenstorage, wherein the compressor comprising a pressure sensor accordingto claim
 1. 13. A method of controlling the peak pressure of thehigh-pressure part of a hydraulic system of a diaphragm compressorpressurising a gas, the diaphragm compressor comprising: an injectionassembly forming part of a hydraulic fluid path between a low-pressurepart of the hydraulic system and the high-pressure part, the injectionassembly comprising: an output valve, a valve, and an injection pumpestablishing a flow of hydraulic fluid from the low-pressure part to thehigh-pressure part when the output valve is open, and a pressure sensorestablishing a feedback signal representing the pressure in thehigh-pressure part, wherein the injection pump establishing a pressurepotential of injection of hydraulic fluid when the valve is closed andwhen the output valve is closed, and wherein a controller is controllingthe pressure potential of injection of hydraulic fluid into thehigh-pressure part, by control of the injection assembly based on thefeedback signal and a hydraulic fluid peak pressure target value of adesired pressure of hydraulic fluid in the high-pressure part.
 14. Amethod according to claim 13, wherein the pressure potential ofinjection of hydraulic fluid is established in the injection assembly.15. A method according to claim 13, wherein the amount of hydraulicfluid injected into the high-pressure part in a compression cycle isdetermined by the established potential of injection of hydraulic fluid,wherein the potential of injection of hydraulic fluid is controlled bycontrolling the valve based on the pressure difference between thepressure represented by the feedback signal and the peak pressure targetvalue.
 16. A method according to claim 13, wherein the pressure isincreased during a plurality of compression cycles following thecompression cycle during which the feedback signal representing thepressure of the high-pressure part was below the peak pressure targetvalue.
 17. A method according to claim 13, wherein the feedback signalrepresenting the pressure in the high-pressure part is measured in eachcompression cycle.
 18. A method according to claim 13, wherein thecontroller is controlling the potential of injection of hydraulic fluidso that the pressure in the high-pressure part is always above areference potential which is equal to or higher than the inlet pressureof the gas.
 19. A method according to claim 13, wherein the feedbacksignal is established by a pressure sensor comprise a housing mounted tothe high-pressure part in which a cylinder with a piston in fluidlyconnection with the hydraulic fluid of the high-pressure part islocated, a displacement member and a displacement sensor, wherein thepressure of the hydraulic fluid in the high-pressure part is physicallydisplacing a displacement member and wherein the size of thedisplacement is measured by a displacement sensor.
 20. A methodaccording to claim 1, wherein the compressor is used for pressurizinghydrogen gas in a high-pressure storage of a hydrogen refueling stationor of a fuel cell vehicle to a pressure above 35 Mpa.